1. Field of the Invention
The present invention relates to a distributed input/output wireless communication system using space-time coding techniques, and more particularly to a method of allocating transmission power based on a symbol error rate for orthogonal space-time block codes (OSTBC).
2. Description of the Related Art
In wireless technology, spatial multiplexing and space-time coding techniques have been relatively recently developed. A certain type of space-time coding, which is referred to as MIMO for multiple-input multiple-output, uses multiple antennas for receiving/transmitting a signal Each of the multiple radio waves can be independently transmitted within a common frequency range for a common time.
In general, MIMO technology generates parallel spatial data streams within a common frequency bandwidth, which is based on using spatially separated antennas. In the transmission of radio waves (even if individual signals are transmitted within a common frequency) statistically independent (i.e. effectively separated) multiple communication channels can be generated by division and demodulation at a receiver. A standard wireless communication system prohibits multipath (i.e. multiple signals that are delayed in time, adjusted in amplitude/phase, and have a common frequency). In contrast, MIMO can depend on multipath signals of little correlation (or weak correlation). Consequently, MIMO can achieve an improved signal-to-noise ratio and higher throughput within a proper frequency bandwidth.
In a certain application of a MIMO-type technology, theoretical results provided by the below mentioned references [1] and [2] have proved distributed antennas (DAs) to be superior to co-located multiple-input multiple-output (C-MIMO) channels in terms of capacity. However, thorough research on a method of taking advantage of the capacity of the DAs has not been done yet. A concept of a distributed wireless communication system (DWCS) is proposed in the below mentioned reference [3]. The system is expected to greatly improve system capacity because the system can process a transmission and receiving signal at once.
OSTBC (See reference [4]) of various space-time codes is very useful for an actual system arrangement due to a simple process of coding and decoding. In future wireless communication, a bottleneck situation may occur in transmission of downlink data. Thus it is important to design optimum downlink OSTBC based on estimation of channel state information (CSI) of a particular transmitter. However, in an OSTCB scheme on DAs, allocation of transmission power is very important because large-scale fading of each of the DAs may be greatly changed.
FIG. 1 is a block diagram illustrating a system for transmitting OSTBC on conventional C-MIMO channels. A data symbol transmitted from a transmitter (i.e. a base station) is modulated by a designated modulation process. It is input to a space-time encoder 100, encoded in space-time, and transmitted to a receiver (i.e. a mobile terminal) 120 through multiple co-located transmitting antennas 110. Here, the receiver 120 has m receiving antennas.
As shown in the FIG. 1, the present research on OSTBC is mainly limited to C-MIMO channels. In this case, open-loop transmission (the same power allocation) is mainly selected, because large-scale fading of each of transmitting antennas is almost the same.
However, this process has a number of limitations. For example, macro diversity cannot be utilized due to co-location of transmitting antennas and an average access distance is much greater than DAs.